Articles
SENSITIVITY AND INVOLVEMENT OF PLANT GROWTH REGULATORS IN DIFFERENTIATION AND MORPHOGENESIS
According to Moore (1989), "cellular differentiation" is the transformation of apparently genetically identical cells into diversified cells, differing biochemical, physiological, and structural attributes; by contrast "morphogenesis" is the integration and coordination of growth and differentiation, occurring at the cellular level, determining morphological characters and gross form.
Plant growth regulators (PGRs) regulate plant growth, differentiation and morphogenesis probably by exerting their influence on particular metabolic reactions in the target tissue via receptor molecules.
This report considers the way in which Plant Growth Regulators, applied to plants or to in vitro explants, facilitate the differentiation and morphogenesis of shoots, roots and flowers.
It also examines the way in which physiological state and genetic environmental conditions influence the activity of PGRs.
Differentiated cells pass first to the dedifferentiation phase, then to induction and finally into differentiation phase.
There is a weak correlation between hormone concentration, measured in the tissue, and the response of the tissue.
This weak correlation has led to controversy as to whether differentiation is regulated by changes in the concentration of PGRs or by changes in the sensitivity of tissues to PGRs (Trewavas, 1983). Although litte is known about the sensitivity of tissues to hormones it seems possible that there could be changes in the concentration of hormone receptors, in receptor affinity or in the activity of hormones or factors (Firn, 1986).
Several attempts have been made in vitro to find suitable explants more responsive to PGRs in promoting morphogenesis (Durzan, 1986; Rugini and Orlando 1992). PGRs usually are added to explants through the media or during culture in cell suspension or in a high dose at the beginning of culture before being placed in a medium lacking PGRs.
Balance is complicated by the correlation lost upon excision of the explants’ wounding reactions, level of inhibitors and by PGR coverage (Durzan, 1987).
Type of PGRs. The PGRs most commonly used in fruit plants are auxins and cytokinins; these can be natural or synthesized.
Ethylene, abscisic acid, polyamines and oligosaccharins are used increasingly for controlling differentiation and morphogenesis.
Type of PGRs used depends primarily on the tissue age, type and sensitivity.